1. Field of the Invention
The present invention relates to a compound semiconductor substrate used in manufacturing a light emitting device and a method for manufacturing the same, and in particular, to a method for manufacturing a compound semiconductor substrate, which is capable of manufacturing a semiconductor substrate having a compound semiconductor layer grown on a metal layer easily and inexpensively, and to a compound semiconductor substrate and a compound semiconductor device manufactured thereby.
2. Description of the Related Art
Gallium nitride (GaN) as a typical compound semiconductor is known as a material suitable for application to a blue light emitting device or a high temperature electronic device. Recently, as the blue light emitting device is a sharp rise in demand, a demand for a GaN substrate is increasing. However, a high quality GaN substrate is very difficult to manufacture, and thus requires much manufacturing cost and time. For examples, an ELO (Epitaxial Lateral Overgrowth) method used widely in manufacturing a high quality GaN substrate uses a SiO2 mask of a stripe shape to reduce stress that is caused by differences in lattice constant and thermal expansion coefficient between a substrate and a GaN crystal. That is, the ELO method grows a GaN film on a substrate, takes the substrate having the grown GaN film out of a reactor, charges the substrate in a deposition equipment to form a SiO2 film on the GaN film, takes the substrate having the deposited SiO2 film out of the deposition equipment, forms a SiO2 mask pattern using photolithography, and charges the substrate in the reactor again to form a GaN layer (for more information, see Korean Patent No. 455277). However, disadvantageously the ELO method goes through a complex process as mentioned above, requires much process time, and has problems in reproductibility and yield.
Meanwhile, it is also an important issue to achieve improvement of light emitting efficiency or reduction of power consumption of a light emitting device manufactured using the above-mentioned compound semiconductor. That is, light generated from an active layer of a light emitting device is emitted toward a surface of the light emitting device and besides is emitted toward a substrate, so that the light is absorbed by the substrate, thereby reducing a light emitting efficiency. To solve the problem, an attempt is made to reflect scatteringly the light that is generated from the active layer and emitted toward the substrate, using a patterned substrate to reduce penetration or absorption by the substrate, thereby increasing a light emitting efficiency toward the surface of the light emitting device. However, this attempt has disadvantages of a complex process and much time required to make the patterned substrate.
And, U.S. Pat. No. 6,239,005 suggests a technique for forming an epitaxial platinum layer on a surface of a sapphire substrate and growing a GaN layer thereon by metalorganic vapor phase epitaxy. That is, this technique uses the platinum layer both as a reflecting mirror and a lower electrode to achieve improvement of light emitting efficiency and reduction of electrical resistance. However, essentially it is difficult to grow a GaN layer on a metal layer, and thus this U.S. patent uses such a costly process that defines a specific crystal face of an electrically insulating substrate having a single crystal structure as a surface to be layered, epitaxially grows a platinum layer on the specific face in the direction of a specific crystal orientation and epitaxially grows a GaN layer thereon.
As such, actually it requires a costly and complex process such as photolithography to manufacture a high quality compound semiconductor substrate with few crystal defects, and it requires a costly process to achieve improvement of light emitting efficiency and reduction of power consumption. Further, in spite of high cost, problems of low reproductibility and yield are left unsettled.